Tree mortality during drought

Understanding the drivers and mechanisms of tree mortality during drought has significant implications for forest management, especially under the background of global climate change with increasing drought frequency and severity. Tree structures have been identified as an important factor influencing tree mortality during drought, but how it functions remained controversial.Here, we provide the datasets and codes used to examined the influence of canopy structure on tree mortality in the southern Sierra Nevada during the 2012-2016 California drought. These datasets include maps of nearly 1.5 million individual trees, with their species information, tree health conditions during the drought, tree structure features, and environmental attributes. With these, we found that drought-induced tree mortality rate has a “negative-positive-negative” piecewise relationship with tree height, but remains a consistent negative relationship with neighborhood canopy structure. Our analyses further revealed that trees in a structurally complex forest and overshadowed by tall neighboring trees experienced lower mortality rate, likely due to reduced exposure to solar radiation and less water demand from evapotranspiration. Our finding suggests establishing complexity in canopy structure could improve forest resistance to drought.

深入探究干旱期间树木死亡的原因和机制，对于森林管理具有重要意义，尤其是在全球气候变化背景下，干旱频率和严重性不断增加的情形下。树木结构已被确认为影响干旱期间树木死亡的重要因素，但其作用机制仍存在争议。在本研究中，我们提供了用于分析2012-2016年加利福尼亚干旱期间南部内华达山脉树木死亡率受冠层结构影响的数据集和代码。这些数据集包括近150万棵树木的地图，以及它们的物种信息、干旱期间的树木健康状况、树木结构特征和环境属性。通过对这些数据的分析，我们发现由干旱引起的树木死亡率与树木高度之间存在“负-正-负”的分段关系，但与邻近冠层结构保持一致的负相关关系。进一步的分析揭示，结构复杂且被高大邻近树木遮蔽的树木死亡率较低，这可能是由于减少了太阳辐射的暴露和降低的蒸散作用对水分的需求。我们的研究结果提示，通过构建复杂的冠层结构，可以增强森林对干旱的抵抗能力。